Esterification of fatty acids



CATION 0F FATTY i Ernst Wecker, Heilbronn-on-the-Neckar, Germany, assignor to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main, Germany No Drawing. Application October 16,

Serial No. 489,236, and in Germany November 10 Claims.

The present invention relates to the esterification of fatty acids.

In order to obtain a quantitative esterification of fatty acids, or mixtures thereof, with gly cerine' it has been already suggested to carry out the esterification with a quantity of glycerine exceeding that necessary for a complete esterification, but in this case mixtures of monoand di-esters are formed together with the neutral tri-esters. If a quantity of acids exceeding that necessary for a complete esterification of the glycerol be employed only some portion of the acids is esterified and especially that which is more easily esterified.

I have found that in the esterification of the long chain fatty acids, 1. e. the acids from fats and oils of vegetal, i. e. vegetable and animal, origin, or the synthetic, equivalent mixtures of carboxylic acids from the destructive oxidation of paraffin wax and similar high molecular hydrocarbons or hydrocarbon mixtures and mixtures containing these fatty acids, with polyhydric aliphatic alcohols it is advantageous to Work first with a quantity of the alcohol desired as for example glycerine, exceeding that required for the complete esterification of the quantity of fatty acid employed, then to provide for a quantity of fatty acid in the reaction mixture that there is an excess of fatty acid during the further course of the esterification above the quantity required for complete esterification of the alcohol present. Finally the remainder of fatty acid, after the esterification is completed, can be removed with the aid of a physical purifying method which is not injurious to the esters obtained as for example by an extraction with ethyl alcohol, by a distillation with the aid of steam or other vaporized inert liquid, preferably in vacuo, by washing the esters with dilute aqueous alkali or any other usual and convenient method.

In this way, especially when esterifying socalled pathologica fatty acids, that is fatty acid mixtures which have changed unfavourably for example when the initial materials, such as seeds, have been'stored for long periods of time so that hydroxy carboxylic acids and acids with an abnormal high molecular weight are formed, it is possible to avoid any enrichment in high molecular and other fatty acids which can only be esterified with difficulty and to avoid any unfavourable infiuence on the properties, as for example the capability of being refined, of the ester obtained. At first mono-esters are mainly formed according to the present invention which are then converted into neutral esters of the polyhydric alcohols.

Thus for example fatty acids of sulphur olive oil or train oil or sanza olive oil fatty acids contain a more or less large proportion of abnormal or high molecular fatty acids which are formed by the fermentation and decomposition of the residues from the pressing of the olives. If the esterification of acids of this nature be carried out so that, in order to obtain tri-glycerides, a quantity of fatty acids exceeding that required for a complete esterification of the quantity of alcohol employed, is present from the start, a kind of fractionation takes place in that the acids which are readily esterified first enter into reaction with the alcohol, as for example glycerine, while the high molecular fatty acids which are diflicult to esterify mainly remain in the esterification residue. For example if a fatty acid mixture having an average molecular weight of 284 be esterified, a mixture of crude fatty acids having an average molecular weight of 347 remains non-esterified. Since the fatty acids which are difiicult to esterify are recovered and returned in circulation to the process, when carrying out the process on a commercial scale an ever increasing enrichment of these acids in the material to be esterified takes place. A further objection is that at the temperatures necessary for the esterification the uncombined, free, normal and especially the abnormal fatty acids tend to polymerize or to form anhydrides, lactones, estolides (esters of two or more molecules of hydroxy carboxylic acids with each other, resembling lactones) and the like, whereby the quality of the resulting ester is injuriously affected.

If the esterification be carried out in the manner hitherto usual exclusively with a quantity of alcohol, as for example glycerine exceeding that required for complete esterification of the acids present, on the one hand the exclusive production of tri-glycerides is impossible and on the other hand the recovery of the excess of alcohol is only possible with great difficulty.

These objections are avoided by carrying out the esterification according to the present invention so that first a quantity of alcohol is used exceeding that required for complete esterification of the acids present whereby the free fatty acids present are practically completely esterified, a further quantity of fatty acids then being added in excess of the amount necessary for the complete esterification of the remainders of nonesterified alcohol. The remainders of free fatty acids consist mainly of normal fatty acids, which in the example hereinbefore given have an average molecular weight of 285, and not of the constituents of the fatty acid mixture which are difficult to esterify, and in this case the subsequent refining is considerably facilitated and at the same time esters having especially advantageous properties are obtained. The recovery of the fatty acids which remain non-esterifled is preferably effected by a treatment of the strongly heated mixture in vacuo with inert liquids, preferably in fine dispersion, such as is described for -example in the specification of my U. S. Patent No. 1,622,126. a

The following examples will further illustrate the nature of this invention but the invention is not restricted vto these examples.

Example 1 1675 kilograms of fatty acidsfrom sanza olive oil having the saponification value 198 are heated within 3 hours to about 240 C. in vacuo, while stirring, with 192 kilograms of 97 per cent glycerine, that is with about 3 per cent more than the amount stoichiometrically necessary for esteriflcation to give tri-glycerides. After this time the reaction comes to a standstill and the content of free fatty acids in the reaction mixture amounts for example to 1.3 per cent. The reaction product has a saponification value of 183 instead of the normal saponification value for olive oil of 189.

After adding a further 40 kilograms of sanza olive oil fatty acids and heating to 240 C. for a further three quarters of an hour, the product has a sapom'fication value of 187 and a content for example of 1.2 per cent of free fatty acids. After the addition of a further 30 kilograms of sanza olive oil fatty acids and heating for another three quarters of an hour at the said temperature 1830 kilograms of a product having the saponification value 189 and a. content for example of 1.9 per cent of freefatty acids of normal character is obtained. The free fatty acids may be separated in the manner already known, as for example by treating the appropriately heated mixture according to the U. S. Patent No. 1,622,126, and supplied for esterification again.

Example 2 1600 kilograms of sulphur olive oil fatty acids having an acid value of 199.3 are heated, while stirring, in vacuo together with 194 kilograms of ethylene glycol, the temperature being raised to 226 C. in the course of 3 hours. After the said temperature has been attained a mixture of the monoand di-esters of the glycol has been formed and the reaction mixture still contains 2.1 per cent of free fatty acids having an acid value of 174.2. After adding further 180 kilograms of the fatty acids heating is continued for 1 hour at 235 C. 1867 kilograms of a product are obtained which contains 1.6 per cent of free acids having an acid value of 198.6 whereas the acids combined with the ethylene glycol have an acid value of 199.4.

What I claim is:

1. In the production of esters from mixtures of fatty acids from fats and oils of vegetal origin, containing diilicultly esterifiable acids formed by decomposition of the said fats and oils, including synthethic, equivalent mixtures, the steps which comprise esterifying the said mixtures with a quantity of a polyhydric aliphatic alcohol exceeding that required for a complete esterification of the quantity of fatty acid employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esteriflcation of the quantity of polyhydric alcohol present and then removing the remainder of free fatty acid.

2. In the production of esters from mixtures of fatty acids from fats and oils of vegetal origin containing difllculty esterifiable acids formed by decomposition of the said fats and oils, the steps which comprise esterifying the said mixtures with a quantity of glycerine exceeding that required for a complete esterification of the quantity of fatty acid employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esteriflcation of the quantity of glycerine present and then physically removing the remainder. of free fatty acid.

3. In the production of esters from mixtures of fatty acids from fats and oils of vegetal origin containing diflicultly esterifiable acids formed by decomposition of the said fats and oils, the steps which comprise esterifying the said mixtures with a quantity of a polyhydric aliphatic alcohol exceeding that required for a complete esteriflcation of the quantity of fatty acid employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esterification of the quantity of polyhydric alcohol present and then distilling off the remainders of free fatty acid by passing a finely divided inert liquid at a pressure below atmospheric pressure through the reaction mass heated to a temperature above the boiling point of the said inert liquid at the said pressure.

4. In the production of esters from mixtures of fatty acids from vegetable oils containing dimcultly esterifiable acids formed by decomposition of the said oils, the steps which comprise esterifying the said mixtures with a quantity of a polyhydric aliphatic alcohol exceeding that required for a complete esterification of the quantity of fatty acids employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esterification of the quantity of polyhydric alcohol present and then removing the remainder of free fatty acid.

5. In the production of esters from mixtures of fatty acids from vegetable oils containing diflicultly esterifiable acids formed by decomposition of the said oils, the steps which comprise esterifying the said mixtures with a quantity-of glycerine exceeding that required for a complete esterification of the quantity of fatty acids employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esterification of the quantity of glycerine present and then removing the remainder of free fatty acid.

6. In the production of esters from mixtures of fatty acids from olive oil containing diflicultly esterifiable acids formed by decomposition of the said oil, the steps which comprise esterifying the said mixtures with a quantity of glycerine exceeding that required for a complete esterification of the quantity of fatty acids employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esterification of the quantity of glycerine present and then removing the remainder of free fatty acid.

7. In the production of esters from mixtures of fatty acids from sanza olive oil, the steps which comprise esterifying the said mixtures with a quantity of glycerine exceeding that required for a complete esterification of the quantity of fatty acids employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esterification of the quantity of glycerine present and then removing the remainder of free fatty acid.

8. In the production of esters from mixtures of fatty acids from sanza olive oil, the steps which comprise esterifying at about 240 C. the said mixtures with a quantity of glycerine exceeding that required for a complete esteriflcation of the quantity of fatty acids employed, heating the product obtained at about 240 C. with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esterification of the quantity of glycerine present and then removing the remainder of free fatty acid by distillation while passing a finely divided inert liquid at a pressure below atmospheric pressure through the reaction mass heated to a temperature above the boiling point of the said inert liquid at the said. pressure.

9. In the production of esters from mixtures of fatty acids from fats and oils of vegetal origin containing dificultly esteriflable acids formed by decomposition of the said fats and oils, the steps which comprise esterifying the said mixtures with a quantity of ethylene glycol exceeding that required for a complete esterification of the quantity of fatty acids employed, heating the product obtained with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esteriflcation of the quantity of ethylene glycol present and then removing the remainder of free fatty acid.

10. In the production of esters from mixtures of fatty acids from sulphur olive oil, the steps which comprise esterifying at about 220 C. the said mixture with a quantity of ethylene glycol exceeding that required for a complete esterification of the quantity of fatty acids employed and heating the product obtained at about 235 C. with a quantity of the aforesaid mixture of fatty acids exceeding that required for a complete esteriflcation of the quantity of ethylene glycol present.

ERNST WECKER. 

